Conventionally, an inkjet printer is designed to perform printing by moving a carriage in the main scanning direction, supplying ink from an ink cartridge to a recording head mounted on the carriage, ejecting ink droplets from the recording head and letting them adhere to (land on) a recording medium, thereby forming an image such as a character or picture consisting of multiple dots.
By the way, in moving the carriage in the inkjet printer, a target velocity that is the velocity targeted by the carriage is set as a target value, and the target velocity is categorized into an acceleration region where the carriage is accelerated from a stopped state, a uniform velocity region where the carriage is moved at a constant velocity, and a deceleration region where the carriage is decelerated and stopped.
In the uniform velocity region, by stably moving the carriage at a constant velocity, the tracks of ink droplets from their ejection from the recording head to their adhesion to the recording medium become uniform, and as the result, dots can be formed in target dot positions on the recording medium. However, if the carriage cannot be stably moved and unevenness occurs in its velocity for example, dots cannot be formed in their target dot positions on the recording medium, degrading the image quality.
Then, in the inkjet printer, feedback control is performed so that the carriage can stably move at a constant velocity in the uniform velocity region.
In the feedback control, based on the above-mentioned target velocity of the carriage, an actual velocity that is the actual velocity of the carriage, a gain, etc., control values including a proportional component and an integral component for the feedback, in other words, feedback control values, are calculated, and the feedback control values are supplied to a carriage driving part for driving the carriage, thereby performing carriage movement control so that the actual velocity becomes the target velocity.
By the way, if an abnormality occurs to the carriage movement, an image cannot be normally formed on the recording medium. For example, if the recording medium hits the carriage, causing a jam, the carriage cannot be moved, and an image cannot be formed on the recording medium. Also, if a foreign body enters inside a chassis of the inkjet printer, the recording medium could become warped, and if the warped recording medium hits the carriage, the carriage cannot be moved at a constant velocity, and dots cannot be formed in the target dot positions on the recoding medium, degrading the image quality.
Then, an inkjet printer has been offered, the inkjet printer being designed to judge whether a deviation between the target velocity and the actual velocity of the carriage has exceeded a threshold value, and if the deviation has exceeded the threshold value, judges that an abnormality has occurred to the carriage movement (see Patent Document 1 for example).